1. Field of the Invention
This invention relates to a method and apparatus for fixation and reduction of spondylolisthesis, e.g., misalignment of the vertebrae comprising the spinal column. More specifically, the present invention relates to a disk cage positioned in the disk space between affected vertebra, and a screw through said vertebra, disk cage and other vertebra and a method utilizing that apparatus.
2. Description of the Related Art
Treatments for conditions involving subluxation of one vertebrae upon another, resulting in misalignment of the spinal column, involve the use of screws which extend through a plate and which are tightened to draw the misaligned vertebrae back into alignment. U.S. Pat. No. 5,531,747 to Ray (hereinafter "Ray") is an example of a plate and screw system for treating spondylolisthesis. Other approaches include insertion of an implant into the disk space between misaligned vertebrae such as shown in U.S. Pat. No. 5,601,556 to Pisharodi (hereinafter "Pisharodi"). The Ray approach has its limitations as discussed in Pisharodi. That patent has a disadvantage in requiring removal of the disk and having multiple steps, that is, two implants are inserted into the disk space only to be substituted later with monolithic implants, Schafer et al., in U.S. Pat. No. 5,800,547 discloses an angled block which is implanted into an intervertebral space. The block includes multiple openings through which securing pins extend after they are pushed into position by a camming mechanism inserted into another opening in the device.
There is, therefore, a need for an improved method of treatment of conditions involving misalignment of the vertebrae of the spinal column, or spondylolisthesis, and it is a principal object of the present invention to provide such a method and an apparatus for use in connection with that method
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. .sctn.1.56(a) exists.